Porokeratotic eccrine ostial and dermal duct nevus of late onset: more frequent than previously suggested?

We describe the case of a 10-year-old boy with a porokeratotic eccrine ostial and dermal duct nevus (PEODDN) of late onset. The patient had an 8-year history of multiple keratotic papules on the dorsal surface, and multiple yellowish pitting lesions on the plantar surface of the right foot. Light-microscopic studies of both lesions showed multiple cornoid lamella-like parakeratotic columns, which exclusively arose over eccrine sweat ducts in which the acrosyringium was dilated. Although PEODDN is considered to be a congenital hamartoma of eccrine origin, a review of the literature showed us that the frequency of a late-onset variant may be as high as 26%.